Probes containing DNA sequences which are complementary to target DNA sequences of specific individual whole chromosomes or regions of chromosomes of a multi-chromosomal genome are known (see, for example, Pinkel et al. in "Fluorescence in situ hybridization with human chromosome-specific libraries: Detection of trisomy 21 and translocations of chromosome 4" at Proc. Nat'l Acad. Sci. USA 85:9138-9142, Dec. 1988; Manuelidis in "Chromosomal Localization of Complex and Simple Repeated Human DNA's" Chromosoma 66:23-32, 1978).
The vast majority of prior art probes prepared from such sequences were indirect label probes and so required post-hybridization processing. Thus, for example, such probes were derivatized with biotin, and, following the hybridization procedure, steps were pursued to build a sandwich-like structure of fluorescein-labeled avidin and biotinylated anti-avidin antibodies. In contrast, the direct label probes of this invention require only one probe penetration step of a slide mounted specimen during an in situ hybridization procedure.
Prior art methods for labeling such prior art chromosome-specific complementary DNA sequences present difficulties in controlling the number of label moieties attached to individual sequences.
Improved probe compositions comprised of (a) fluorophore labels which are easily and accurately directly detected, and (b) DNA segments which are complementary to specific chromosomal DNA segments would be very useful as chromosome specific stains in in situ hybridization assays. The present invention provides both such probes and efficient, reliable methods for their preparation and use.